Scanner having a light beam incident position adjusting device

ABSTRACT

A scanner includes a light-beam emitter for emitting a light beam; a light-beam deflector for deflecting the light beam to scan a scanning surface; a photo-detector provided at a position outside an image-forming scanning range of the scanning surface to detect a scanning light beam before the scanning light beam starts generating a scanning line in the image-forming scanning range; a rotatable member, located in front of an incident surface of the photo-detector, that is rotatable about a rotational axis perpendicular to a plane defined by the scanning light beam by the deflector; an optical member, provided on the rotatable member, that allows the scanning light beam to pass therethrough to be incident upon the incident surface of the photo-detector; and a device for adjusting rotational position of the rotatable member about the rotational axis.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a scanner in which a light beamis deflected to scan a scanning surface, and more specifically to ascanner which is provided with a device for adjusting an incidentposition of a light beam on a photo-detector used for determining thetiming of commencement of writing each scanning line with respect to ascanning surface.

[0003] 2. Description of the Related Art

[0004] A laser-beam printer provided with a laser-beam scanner is wellknown. In a laser-beam printer, a laser beam which is modulated inaccordance with image signals to be output from a laser-beam emitter isdeflected by a polygon mirror to scan a photoconductive surface of aphotoconductive drum in the main scanning direction to thereby form amain scanning line in the photoconductive surface. The laser emission isturned ON and OFF in accordance with given image signals to draw acorresponding image (charge-latent image) on the photoconductive surfaceof the drum, and subsequently this image drawn on the photoconductivesurface of the drum is transferred to plain paper according to aconventional electrophotographic method. Dry powder (e.g., toner) thatadheres only to the charged area is applied to the drum, transferred tothe plain paper and fused by heat. Such a laser-beam printer is widelyused; e.g., as an output device for a computer.

[0005] In a laser-beam scanner provided in such a laser-beam printer, aphoto-detector (i.e., a laser-beam detector) is generally fixed at aposition outside the latent-image-forming scanning range to detect thescanning laser beam before it starts generating each scanning line. Thephoto-detector generates a pulse signal each time the scanning laserbeam is incident on the photo-detector. The pulse signals output fromthe photo-detector are input to a processor, and subsequently theprocessor generates corresponding horizontal synchronizing pulses(HSYNC) to determine the timing of commencement of writing main scanningdata, namely, writing each main scanning line.

[0006] In such a laser-beam scanner, two types of devices for adjustingthe timing of commencement of writing each main scanning line withrespect to the photoconductive surface of the drum (i.e., for adjustingthe timing of generating horizontal synchronizing pulses) are known. Ineach type of adjusting device, a reflecting mirror is arranged at aposition outside the latent-image-forming-scanning range to detect thescanning laser beam before it starts generating each scanning line,while a photo-detector is arranged at a position on the path of thelaser beam reflected by the reflecting mirror. In one type of adjustingdevice, the reflecting mirror is rotatable so that the incident positionof the laser beam on the photo-detector can be adjusted, which makes itpossible to adjust the timing of generating horizontal synchronizingpulses. In the other type of adjusting device, the reflecting mirror isfixed while the photo-detector is linearly movable so that the incidentposition of the laser beam on the photo-detector can be adjusted.

[0007] In the former type of adjusting device, although the incidentposition of the laser beam on the photo-detector can be adjusted byrotating the reflecting mirror, it is difficult to finely adjust theincident position of the laser beam on the photo-detector. Furthermore,the reflective mirror needs to be accurately and precisely positioned ona base on which the reflective mirror is to be mounted. In the lattertype of adjusting device, the position at which the photo-detector is tobe arranged is quite limited. Moreover, in each type of adjustingdevice, in the case where the base on which the reflective mirror andthe photo-detector are mounted is slightly deformed after a long periodof use, the respective positions of the reflective mirror and thephoto-detector deviate from their original positions. In this case, therespective positions of the reflective mirror and the photo-detectorcannot be easily adjusted from outside the laser-beam apparatus.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to provide a scannerprovided with a device for adjusting the incident position of a lightbeam on a photo-detector used for determining the timing of commencementof writing each scanning line with respect to a scanning surface,wherein the adjusting device makes it possible to finely and easilyadjust the incident position of the light beam on the photo-detector.

[0009] Another object of the present invention is to provide a scannerhaving such an adjusting device which makes it possible to finely andeasily adjust the incident position even from outside the scanner.

[0010] Other aspects, objects and advantages of the present inventionwill become apparent to one skilled in the art from the followingdisclosure and the appended claims.

[0011] According to an aspect of the present invention, there isprovided a scanner including a light-beam emitter for emitting a lightbeam; a light-beam deflector for deflecting the light beam to scan ascanning surface; a photo-detector provided at a position outside animage-forming scanning range of the scanning surface to detect ascanning light beam before the scanning light beam starts generating ascanning line in the image-forming scanning range; a rotatable member,located in front of an incident surface of the photo-detector, that isrotatable about a rotational axis perpendicular to a plane defined bythe scanning light beam by the deflector; an optical member, provided onthe rotatable member, that allows the scanning light beam to passtherethrough to be incident upon the incident surface of thephoto-detector; and a device for adjusting rotational position of therotatable member about the rotational axis.

[0012] Preferably, the light-beam deflector includes a polygon mirror.

[0013] Preferably, a signal, output from the photo-detector, is used fordetecting the timing for commencement of writing the scanning line withrespect to the scanning surface.

[0014] The optical member can include a cylindrical lens or aplane-parallel plate. Preferably, the optical member includes a memberhaving an optical axis which lies in a plane defined by the scanninglight beam, and the rotational axis extends perpendicular to the opticalaxis.

[0015] The rotatable member can be positioned in a recess formed in ahousing to be rotatable about the rotational axis.

[0016] In an embodiment, the recess is a circular recess, and therotatable member includes a disc portion which is fitted into thecircular recess to be rotatable about the rotational axis.

[0017] Alternatively, the rotatable member includes a shaft coaxial tothe rotational axis, and the rotatable member is positioned in therecess with the shaft being inserted into a hole formed at the bottom ofthe recess so that the rotatable member is rotatable about the shaft.

[0018] Further, the recess can be formed on an outer surface of thehousing, and a through hole through which the optical member is insertedin the housing is formed at the bottom of said recess, and the rotatablemember is positioned in the recess with the optical member beinginserted into the housing through the through hole.

[0019] For holding the rotatable member at an adjusted position, theadjusting device can include at least one set screw which penetratesinto the rotatable member through a slot formed thereon to be screwedinto the housing.

[0020] Alternatively, it is possible that the adjusting device includesa member, fixed to the housing, for pressing the rotatable memberagainst the bottom of the recess. Preferably, the pressing memberincludes a spring. Further, the spring can be a leaf spring fixed to thehousing by at least one set screw.

[0021] Preferably, the scanner further includes a device for rotatingthe rotatable member about the rotational axis.

[0022] In an embodiment, the rotating device includes a radial slotformed on the rotatable member to extend in a radial direction thereof;and a rotating tool engageable with the rotatable member to rotate therotatable member about the rotational axis. Namely, the tool includes anengaging pin engageable with the radial slot, an axis of the engagingpin deviating from a rotational axis of the rotating tool.

[0023] Alternatively, the rotating device includes a circumferentialgear formed on an outer peripheral surface of the rotatable member; anda rotating tool engageable with the rotatable member to rotate therotatable member about the rotational axis. Namely, the rotating toolincludes a pinon gear which is engaged with the circumferential gear.

[0024] It is preferable that the scanning surface is a photoconductivesurface of a photoconductive drum.

[0025] In an embodiment, the photo-detector and the light-beam emitterare supported on a common circuit substrate and do not relatively move.

[0026] The scanner can include an fθ reflecting lens that reflects thescanning light beam deflected by the light-beam deflector to thescanning surface.

[0027] According to another aspect of the present invention, there isprovided a scanner including a light-beam emitter for emitting a lightbeam; a light-beam deflector for deflecting the light beam to scan ascanning surface; a photo-detector provided at a position outside animage-forming scanning range of the scanning surface to detect ascanning light beam before the scanning light beam starts generating ascanning line, the photo-detector generating an output signal upondetecting the scanning light beam to determine a timing of commencementof writing the scanning line with respect to the scanning surface; andan optical member for deflecting the scanning light beam to be incidenton the photo-detector in a direction to vary the timing of the scanninglight beam incident upon the photo-detector.

[0028] The present disclosure relates to subject matter contained inJapanese Patent Application No. 10-92725 (filed on Mar. 19, 1998) whichis expressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be described below in detail withreference to the accompanying drawings in which:

[0030]FIG. 1 is a perspective view of the scanning optical system of alaser-beam scanner to which the present invention is applied;

[0031]FIG. 2 is a perspective view of an embodiment of a device foradjusting the rotational position of a cylindrical lens with respect toa housing of the laser-beam scanner;

[0032]FIGS. 3A and 3B are explanatory views of the cylindrical lens whenrotated about a rotational axis;

[0033]FIG. 4 is a perspective view of the scanning optical system of alaser-beam scanner in which a photo-detector and a light-beam emitterare supported on a common circuit substrate;

[0034]FIG. 5 is an exploded perspective view of another embodiment ofthe device for adjusting the rotational position of the cylindricallens;

[0035]FIG. 6 is a plan view of still another embodiment of the devicefor adjusting the rotational position of the cylindrical lens;

[0036]FIG. 7 is a plan view of yet another embodiment of the device foradjusting the rotational position of the cylindrical lens;

[0037]FIG. 8 is a plan view of yet another embodiment of the device foradjusting the rotational position of the cylindrical lens;

[0038]FIG. 9 is a plan view of yet another embodiment of the device foradjusting the rotational position of the cylindrical lens;

[0039]FIG. 10 is a perspective view of an embodiment of a device forrotating the cylindrical lens; and

[0040]FIG. 11 is a perspective view of another embodiment of the devicefor rotating the cylindrical lens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041]FIG. 1 shows the scanning optical system of a laser-beam scannerto which the present invention is applied. The laser-beam scanner scansthe photoconductive surface of a photoconductive drum 1 (scanningsurface). The laser beam scanner and the photoconductive drum 1 arepositioned within a laser-beam printer as essential elements.

[0042] The scanning optical system of the laser-beam scanner is providedwith a laser diode (light-beam emitter) 2, a collimating lens 4 a, acylindrical lens 4 b, a reflecting mirror 6, a polygon mirror(light-beam deflector) 8, an fθ reflecting lens 10, an fθ lens 12, areflecting mirror 14, a cylindrical lens (optical member) 16, and alaser-beam detector (photo-detector) 18. The collimating lens 4 a andthe cylindrical lens 4 b together constitute an optical system 4 for thelaser diode 2.

[0043] The laser diode 2 outputs a laser beam L1 modulated in accordancewith image signals. The laser beam emitted from the laser diode 2 iscollimated through the collimating lens 4 a. Thereafter, this collimatedlaser beam is made incident upon the cylindrical lens 4 b positioned infront of the collimating lens 4 a. The cylindrical lens 4 b has power inthe sub-scanning direction, so that the spot of the laser beam incidentthereon is converged therethrough in the sub-scanning direction to beincident upon the reflecting mirror 6. The laser beam which is incidenton the reflecting mirror 6 is reflected thereby to be incident on thepolygon mirror 8. The polygon mirror 8 is driven to rotate at a fastrotational speed by a motor (not shown), so that the laser beam incidenton the polygon mirror 8 is deflected in the main scanning direction tobe incident on the fθ reflecting lens 10.

[0044] The deflected laser beam L2 which is incident on the fθreflecting lens 10 to be reflected thereby proceeds to the reflectingmirror 20 through the fθ lens 12, which is arranged to face the freflecting lens 10. Subsequently, the laser beam incident upon thereflecting mirror 20 is reflected thereby towards the photoconductivesurface of the drum 1.

[0045] The polygon mirror 8 rotates in a counterclockwise direction(shown by an arrow “A”), as viewed in FIG. 1. The reflecting mirror 14is fixed at a position to receive the scanning laser beam emitted fromthe polygon mirror 8 before the scanning laser beam is incident on thefθ reflecting lens 10 at each scanning sweep while the polygon mirror 8rotates. The laser beam L3 reflected by the reflecting mirror 14 isincident on the laser-beam detector 18 through the cylindrical lens 16.The laser-beam detector 18 is fixed at a position facing to thereflecting mirror 14 with the cylindrical lens 16 being positionedbetween the reflecting mirror 14 and the laser-beam detector 18. Namely,the cylindrical lens 16 is located in front of an incident surface ofthe laser-beam detector 18.

[0046] The laser-beam detector 18 outputs a pulse signal for detectingthe timing of commencement of writing each scanning line with respect tothe photoconductive surface of the drum 1 each time the laser beam L3 isincident on the laser-beam detector 18.

[0047] As shown in FIG. 2 the cylindrical lens 16 is fixed onto arotatable base (rotatable member) 22 which is mounted on the housing 26of the laser-beam scanner to be rotatable about a rotational axis 16 arelative to the housing 26. The scanning optical system shown in FIG. 1is enclosed in the housing 26. The rotational axis 16 a extendsperpendicular to the optical axis of the cylindrical lens 16 and thedirection (path) of the laser beam L3. Note that, in this embodiment,the optical axis of the cylindrical lens 16 lies in a plane that isdefined by the scanning light beam emitted from the polygon mirror 8.

[0048] The cylindrical lens 16 can be rotated about the rotational axis16 a to deflect the laser beam L3 which passes therethrough so as toshift the same substantially in parallel on a plane which isperpendicular to the rotational axis 16 a to thereby either delay oradvance the timing of the incident laser beam L3 on the laser-beamdetector 18. Accordingly, the timing of commencement of writing eachscanning line with respect to the photoconductive surface of the drum 1can be adjusted by rotating the cylindrical lens 16.

[0049] The rotatable base 22, onto which the cylindrical lens 16 ismounted, is provided with a disc portion 221 and a shaft 224 which isformed integral with the disc portion 221. The rotatable base 22 isconnected to the housing 26 so that the disc portion 221 is rotatablyfitted in a circular recess 222 with the shaft 224 being rotatablyfitted into a hole 223 formed at the center of the bottom of thecircular recess 222. With this structure, the rotatable base 22 isrotatable about the shaft 224 with respect to the housing 26 so that thecylindrical lens 16 can rotate about the rotational axis 16 a.

[0050] The rotatable base 22 is provided with a circumferential slot 241which extends circumferentially about the rotational axis 16 a. A setscrew 242 is inserted into the circumferential slot 241 so that the setscrew 242 is screw-engaged with a female screw hole 243 formed at thebottom of the circular recess 222. The rotatable base 22 can be rotatedabout the rotational axis 16 a on the housing 26 when the set screw 242is loosened while the rotatable base 22 cannot be rotated about therotational axis 16 a on the housing 26 when the set screw 242 is tightlyfastened. Accordingly, the circumferential slot 241, the set screw 242and the female screw hole 243 together constitute an adjusting device 24for adjusting the rotational position of the cylindrical lens 16 aboutthe rotational axis 16 a and for fixing the same with respect to thehousing 26.

[0051] In the laser-beam scanner having such a structure, the laser beamL1 emitted from the laser diode 2 is incident upon the reflected mirror6 via the collimating lens 4 a and the cylindrical lens 4 b.Subsequently, the laser beam L1 is reflected by the reflected mirror 6to be incident upon the polygon mirror 8. The polygon mirror 8 has aregular hexagonal cross section and is provided along a circumferencethereof with six reflecting surfaces (scanning laser beam deflectingsurfaces). The laser beam reflected by the reflecting mirror 6 to beincident on the polygon mirror 8 is reflected by each of the sixreflecting surfaces while the polygon mirror 8 rotates. The laser beamreflected by the polygon mirror 8 is incident on the fθ reflecting lens10. The laser beam L2 reflected by the fθ reflecting lens 10 to proceedtowards the fθ lens 12 passes therethrough to be reflected by thereflecting mirror 20 to thereby proceed towards the photoconductivesurface of the drum 1. The laser diode 2 is controlled to turn its laseremission ON and OFF in accordance with given image data to draw acorresponding image (charge-latent image) on the photoconductive surfaceof the drum 1; and subsequently, the image drawn on the photoconductivesurface of the drum 1 is transferred to plain paper according to aconventional electrophotographic method.

[0052] The polygon mirror 8 is rotated at a fast rotational speed in thedirection of the arrow “A” shown in FIG. 1, so that the incident angleof the laser beam L1 on each reflecting surface of the polygon mirror 8varies. Hence, the laser beam L2 is deflected by the polygon mirror 8 inthe main scanning direction (indicated by an arrow B in FIG. 1).

[0053] The laser beam L3 which is incident on the fθ reflecting lens 10to be reflected by the reflecting mirror 14 proceeds towards thecylindrical lens 16 rather than the fθ lens 12. As described the above,when the laser beam L3 passes through the cylindrical lens 16, the laserbeam L3 which proceeds towards the laser-beam detector 18 is deflectedto shift substantially in parallel on a plane which is perpendicular tothe rotational axis 16 a. Namely, when the laser beam L3 passes throughthe cylindrical lens 16, the laser beam L3 which proceeds towards thelaser-beam detector 18 is deflected in a direction to either delay oradvance the timing of commencement of writing each scanning line withrespect to the photoconductive surface of the drum 1.

[0054] Each time the laser beam L3 is incident on the laser-beamdetector 18, the laser-beam detector 18 outputs a pulse signal. Thepulse signals output from the laser-beam detector 18 are input to aprocessor (not shown), and subsequently, the processor generatescorresponding horizontal synchronizing pulses (HSYNC) to determine thetiming of commencement of writing main scanning data; i.e. each mainscanning line.

[0055] The horizontal synchronizing pulses are input to a clockgenerator so that it synchronously generates corresponding clock pulses.Subsequently the clock pulses are input to a memory for storing imagedata, and the stored image signals are sequentially read out of thememory in accordance with the input close pulses. The laser diode 2outputs the laser beam L1 which is modulated in accordance with theimage signals read out of the memory.

[0056] The way of adjusting the angular position of the cylindrical lens16 to deflect the incident laser beam so as to delay or advance thetiming of commencement of writing each scanning line with respect to thephotoconductive surface of the drum 1 will be hereinafter discussed.

[0057] First of all, the rotatable base 22 having the cylindrical lens16 mounted thereon needs to be fitted in the circular recess 222, withthe shaft 224 being fitted into the hole 223 and with the set screw 242being engaged with the female screw hole 243 through the circumferentialslot 241.

[0058] In this state, the set screw 242 is loosened and subsequently therotatable base 22 is slightly rotated clockwise or counterclockwiseabout the shaft 224, i.e., the rotational axis 16 a.

[0059] In the case where the cylindrical lens 16 is rotated clockwise asviewed in FIG. 3A from the position shown by a solid line to theposition shown by a dotted line, the laser beam L3 incident on thelaser-beam detector 18 is deflected to shift to the left from theposition shown by a solid line to the position shown by a two-dottedchain line in FIG. 3A. When the polygon mirror 8 is rotated, the laserbeam L3 is scanned (moved) from right to left in FIGS. 3A and 3B.Accordingly, the rotation of the cylindrical lens 16 as shown in FIG. 3Acauses the laser-beam detector 18 to delay the output of a pulse signalto thereby delay the timing of commencement of writing each scanningline with respect to the photoconductive surface of the drum 1.

[0060] On the other hand, in the case where the cylindrical lens 16 isrotated counterclockwise as viewed in FIG. 3B from the position shown bya solid line to the position shown by a dotted line, the laser beam L3incident on the laser-beam detector 18 is deflected to shift to theright from the position shown by a solid line to the position shown by atwo-dotted chain line in FIG. 3B. This makes the laser-beam detector 18to advance the output of a pulse signal to thereby advance the timing ofcommencement of writing each scanning line with respect to thephotoconductive surface of the drum 1.

[0061] After the adjustment of the timing of commencement of writingeach scanning line is completed, the set screw 242 is tightly fastenedto fix the disc portion 221 to the circular recess 222 of the housing26, which completes the adjusting operation. The cylindrical lens 16,the rotatable base 22, the circular recess 222 and the adjusting device24 together constitute a light beam incident position adjusting device.

[0062] It can be appreciated from the foregoing that the incidentposition of the laser beam L3 with respect to the laser-beam detector 18can be easily and precisely adjusted by rotating the rotatable base 22about the rotatable axis 16 a. Hence, with the light beam incidentposition adjusting device, the timing of commencement of writing eachscanning line with respect to the photoconductive surface of the drum 1can be easily and precisely adjusted by rotating the rotatable base 22about the rotatable axis 16 a.

[0063]FIG. 4 shows an embodiment in which, so as not to relatively move,the laser-beam detector 18′ (photo-detector) and the laser diode 2′(light-beam emitter) are supported on a common circuit substrate 100. Inthis construction, since the laser-beam detector 18′ is fixed to thesubstrate 100, the type of adjusting device that moves thephoto-detector (i.e., the laser-beam detector 18′) cannot be used.However, in the above-described adjusting device of the presentinvention, the cylindrical lens 16 is rotated in order to performadjustment; therefore, the timing of the incident laser beam L3 on thelaser-beam detector 18′ can be adjusted regardless of the type ofphoto-detector being utilized.

[0064] The device for adjusting the rotational position of thecylindrical lens 16 (and fixing the cylindrical lens 16 to the housing26) is not limited solely to the particular aforementioned device (i.e.,the adjusting device 24) but can be any other device as long as it bearsa similar function. FIG. 5 shows another embodiment of the adjustingdevice for adjusting the rotational position of the cylindrical lens 16.In this embodiment the housing 26 is provided on a bottom surfacethereof with a circular recess 222′ which corresponds to the circularrecess 222 of the previous embodiment. A circular through hole 225through which the cylindrical lens 16 can be inserted in the housing 26is formed at the center of the bottom of the circular recess 222′. Arotatable base 22′, which corresponds to the rotatable base 22 of theprevious embodiment, is not provided with a shaft which corresponds tothe shaft 224 of the rotatable base 22. When the rotatable base 22′ isset on the housing 26, the disc portion 221 of the rotatable base 22′ isrotatably fitted in the circular recess 222′ with the cylindrical lens16 being inserted into the housing 26 through the through hole 225. Withsuch a adjusting (fixing) device, the cylindrical lens 16 can be fixedto the housing 26 in place from outside the housing 26, which makes iteasier to set the cylindrical lens 16 on the housing 26.

[0065] In the aforementioned embodiments, the rotatable base 22 (or 22′)is fixed to the housing 26 using only one set screw 242. However, therotatable base 22 (or 22′) can be fixed to the housing using more thanone set screw. FIG. 6 shows another embodiment using two set screws 242to fix the disc portion 221 of the rotatable base 22 to the housing 26.FIG. 7 shows yet another embodiment using three set screws 242 to fixthe disc portion 221 of the rotatable base 22 to the housing 26. In FIG.6 the two set screws 242 are positioned on respective sides with respectto the path of the laser beam L3 so as to face respective ends (rightand left ends as viewed in FIG. 6) of the cylindrical lens 16. In FIG. 7the three set screws 242 are positioned at regular intervals in acircumferential direction of the disc portion 221.

[0066]FIG. 8 shows another embodiment of the adjusting device foradjusting the rotational position of the cylindrical lens 16. In thisembodiment the disc portion 221 is fixed to the housing 26 by aadjusting device 30 which is composed of a leaf spring 302 and two setscrews 303 for securing the leaf spring 302 to the housing 26. The leafspring 302 has a substantially rectangular shape and is provided at acenter thereof with a circular hole 301 in which the cylindrical lens 16is positioned. The longitudinal length of the leaf spring 302 is largerthan the diameter of the disc portion 221 so as to press the sameagainst the housing 26. The leaf spring 302 is provided, on a surfacethereof facing the disc portion 221, with two projections 304 which arepositioned on respective sides with respect to the cylindrical lens 16to be aligned along the path of the laser beam L3, as can be seen inFIG. 8. The leaf spring 302 is further provided at respective endsthereof with two slits through which the two set screws are respectivelyinserted to be screwed into the housing 26. In a state where the leafspring 302 is tightly secured to the housing 26 by the set screws 303,the two projections 304 of the leaf spring 302 come into pressingcontact with the disc portion 221, so that the disc portion 221 istightly held between the leaf spring 302 and the housing 26, so that thedisc portion 221 is fixed to the housing 26.

[0067]FIG. 9 shows yet another embodiment of the adjusting device foradjusting the rotational position of the cylindrical lens 16. In thisembodiment the disc portion 221 is fixed to the housing 26 by aadjusting device 40 which includes a leaf spring 402 and a set screw 403for securing the leaf spring 402 to the housing 26. The leaf spring 402has a substantially U-shape and is provided with two parallel projectingportions 401 between which the cylindrical lens 16 is positioned. Theprojecting portions 401 are positioned on respective sides relative tothe path of the laser beam L3, as can be seen in FIG. 9. Each projectingportion 401 is provided, at its tip on a surface thereof facing the discportion 221, with a projection 404. In a state where the leaf spring 402is tightly secured to the housing 26 by the set screw 403, the twoprojections 404 of the leaf spring 402 come into pressing contact withthe disc portion 221, so that the disc portion 221 is tightly heldbetween the leaf spring 402 and the housing 26, so that the disc portion221 is fixed to the housing 26.

[0068]FIG. 10 shows an embodiment of device for rotating the cylindricallens 16. In this embodiment, the cylindrical lens 16 is positioned inplace by inserting the same into the housing 26 from outside the housing26, and the operation of rotating the cylindrical lens 16 can be carriedout from outside the housing 26.

[0069] In this embodiment, similar to the embodiment shown in FIG. 5,the housing 26 is provided on a bottom surface thereof with a circularrecess 222′. A circular through hole 225 through which the cylindricallens 16 can be inserted in the housing 26 is formed at the center of thebottom of the circular recess 222′. The disc portion 221 of thisembodiment is provided with two circumferential slots 241 for fixing thedisc portion 221 to the housing 26 by two set screws 242 respectivelyinserted into the two circumferential slots 241. The disc portion 221 isfurther provided with a radial slot 601 which extends in a radialdirection of the disc portion 221. The disc portion 221 is rotatablyfitted in the circular recess 222′ with the cylindrical lens 16 beinginserted into the housing 26 through the through hole 225. A tool 603 isused to rotate the cylindrical lens 16. The tool 603 is provided at thetip thereof with an engaging pin 602 which can be inserted into theradial slot 601. The axis of the engaging pin 602 extends parallel with,but deviates from, the rotational axis of the tool 603, so that the discportion 221 is rotated when the tool 603 rotates about its rotationalaxis with the engaging pin 602 being inserted into the radial slot 601.Each set screw 242 needs to be loosened in advance when the disc portion221 is rotated by the tool 603. The slot 601 and the tool 603 togetherconstitute a device 60 for externally rotating the cylindrical lens 16.

[0070] In a state where the engaging pin 602 is engaged with the radialslot 601, rotating the tool 603 without moving the same in a radialdirection thereof causes the disc portion 221 (the cylindrical lens 16)to rotate clockwise or counterclockwise in a direction shown by an arrowin FIG. 10. Hence, with the use of the device 60, the incident positionof the laser beam L3 on the laser-beam detector 18 can be finely andeasily adjusted even from outside the housing 26 of the scanner. Afterthe adjusting operation (i.e., the rotation of the cylindrical lens 16)is completed, the tool 603 is disengaged from the disc portion 221 andsubsequently each set screw 242 is tightly fastened to fix the discportion 221 to the circular recess 222′ of the housing 26, whichcompletes the adjusting operation.

[0071]FIG. 11 shows another embodiment of a device for rotating thecylindrical lens 16. In this embodiment, similar to the previousembodiment shown in FIG. 10, the cylindrical lens 16 is positioned inplace by inserting the same into the housing 26 from outside the housing26, and the operation of rotating the cylindrical lens 16 can be carriedout from outside the housing 26. The housing 26 is provided on a bottomsurface thereof with a circular recess 222′. A circular through hole 225through which the cylindrical lens 16 can be inserted in the housing 26is formed at the center of the bottom of the circular recess 222′. Thedisc portion 221 of this embodiment is provided with two circumferentialslots 241 for fixing the disc portion 221 to the housing 26 by two setscrews 242 respectively inserted into the two circumferential slots 241.The disc portion 221 is further provided on an outer peripheral surfacethereof with a circumferential gear 701. The disc portion 221 isrotatably fitted in the circular recess 222′ with the cylindrical lens16 being inserted into the housing 26 through the through hole 225. Thehousing 26 is provided with a small circular recess 226 which isconnected with the circular recess 222′. In this embodiment a tool 703is used to rotate the cylindrical lens 16. The tool 703 is provided atthe tip thereof with a pinion gear 702 which can be fitted in the smallcircular recess 226. The pinion gear 702 meshes with the circumferentialgear 701 of the disc portion 221 when the pinion gear 702 is fitted inthe small circular recess 226. Each set screw 242 needs to be loosenedin advance when the disc portion 221 is rotated by the tool 703. Thecircumferential gear 701, the tool 703 and the small circular recess 226together constitute a device 70 for rotating the cylindrical lens 16.

[0072] The pinion gear 702 is engaged with the circumferential gear 701by inserting the pinion gear 702 into the small circular recess 226 whenthe cylindrical lens 16 needs to be rotated. In a state where the piniongear 702 is engaged with the circumferential gear 701, rotating the tool703 causes the disc portion 221 (the cylindrical lens 16) to rotateclockwise or counterclockwise in a direction shown by an arrow in FIG.11. Hence, with the use of the device 70, the incident position of thelaser beam L3 on the laser-beam detector 18 can be finely and easilyadjusted even from outside the housing 26 of the scanner. After theadjusting operation (i.e., rotation of the cylindrical lens 16) iscompleted, the tool 703 is taken out of the small circular recess 226 ofthe housing 26 and subsequently each set screw 242 is tightly fastenedto fix the disc portion 221 to the circular recess 222′ of the housing26, which completes the adjusting operation.

[0073] In each of the aforementioned embodiments, although thecylindrical lens 16 as an optical member is fixed to the disc portion221, the cylindrical lens 16 can be replaced by a plane-parallel plateto attain a similar effect. FIGS. 3A and 3B show a sectional portion ofthe cylindrical lens 16; the sectional portion of the cylindrical lens16 does not have any power in scanning (beam shifting) direction (rightto left in FIGS. 3A and 3B) with respect to the laser-beam detector 18.In view of this aspect, if this sectional portion is replaced by anequivalent plane-parallel plate that does not have any power in thescanning direction, a similar beam-shifting effect as shown in FIGS. 3Aand 3B is carried out by rotating the plane-parallel plate. However, acylindrical lens 16 is used in the above-described embodiment as thecylindrical lens facilitates collection of the laser beam L3 onto thelaser-beam detector 18.

[0074] Obvious changes may be made in the specific embodiments of thepresent invention described herein, such modifications being within thespirit and scope of the invention claimed. It is indicated that allmatter contained herein is illustrative and does not limit the scope ofthe present invention.

What is claimed is:
 1. A scanner comprising: a light-beam emitter foremitting a light beam; a light-beam deflector for deflecting said lightbeam to scan a scanning surface; a photo-detector provided at a positionoutside an image-forming scanning range of said scanning surface todetect a scanning light beam before said scanning light beam startsgenerating a scanning line in said image-forming scanning range; arotatable member located in front of an incident surface of saidphoto-detector, said rotatable member being rotatable about a rotationalaxis perpendicular to a plane defined by said scanning light beam bysaid deflector; an optical member that is provided on said rotatablemember, said optical member allowing said scanning light beam to passtherethrough to be incident upon said incident surface of saidphoto-detector; and a device for adjusting rotational position of saidrotatable member about said rotational axis.
 2. The scanner according toclaim 1, wherein said light-beam deflector comprises a polygon mirror.3. The scanner according to claim 1, wherein a signal, output from saidphoto-detector, is used for detecting the timing for commencement ofwriting said scanning line with respect to said scanning surface.
 4. Thescanner according to claim 1, wherein said optical member comprises acylindrical lens.
 5. The scanner according to claim 1, wherein saidoptical member comprises a plane-parallel plate.
 6. The scanneraccording to claim 1, wherein said optical member comprises a memberhaving an optical axis which lies in said plane defined by said scanninglight beam and wherein said rotational axis extends perpendicular tosaid optical axis.
 7. The scanner according to claim 1, wherein saidrotatable member is positioned in a recess formed in a housing to berotatable about said rotational axis.
 8. The scanner according to claim7, wherein said recess is a circular recess, and wherein said rotatablemember comprises a disc portion which is fitted into said circularrecess to be rotatable about said rotational axis.
 9. The scanneraccording to claim 7, wherein said rotatable member comprises a shaftcoaxial to said rotational axis, and wherein said rotatable member ispositioned in said recess with said shaft being inserted into a holeformed at the bottom of said recess so that said rotatable member isrotatable about said shaft.
 10. The scanner according to claim 7,wherein said recess is formed on an outer surface of said housing, andwherein a through hole through which said optical member is inserted insaid housing is formed at the bottom of said recess, and wherein saidrotatable member is positioned in said recess with said optical memberbeing inserted into said housing through said through hole.
 11. Thescanner according to claim 7, wherein said adjusting device comprises atleast one set screw which penetrates into said rotatable member througha slot formed thereon to be screwed into said housing.
 12. The scanneraccording to claim 7, wherein said adjusting device comprises a member,fixed to said housing, for pressing said rotatable member against thebottom of said recess.
 13. The scanner according to claim 12, whereinsaid pressing member comprises a spring.
 14. The scanner according toclaim 13, wherein said spring comprises a leaf spring fixed to saidhousing by at least one set screw.
 15. The scanner according to claim 1,further comprising a device for rotating said rotatable member aboutsaid rotational axis.
 16. The scanner according to claim 15, whereinsaid rotating device comprises: a radial slot formed on said rotatablemember to extend in a radial direction thereof; and a rotating toolengageable with said rotatable member to rotate said rotatable memberabout said rotational axis, wherein said tool comprises an engaging pinengageable with said radial slot, an axis of said engaging pin deviatingfrom a rotational axis of said rotating tool.
 17. The scanner accordingto claim 15, wherein said rotating device comprises: a circumferentialgear formed on an outer peripheral surface of said rotatable member; anda rotating tool engageable with said rotatable member to rotate saidrotatable member about said rotational axis, said rotating toolcomprising a pinon gear which is engaged with said circumferential gear.18. The scanner according to claim 1, wherein said scanning surface is aphotoconductive surface of a photoconductive drum.
 19. The scanneraccording to claim 1, wherein said photo-detector and said light-beamemitter are supported on a common circuit substrate and do notrelatively move.
 20. The scanner according to claim 1, furthercomprising an fθ reflecting lens that reflects said scanning light beamdeflected by said light-beam deflector to said scanning surface.
 21. Ascanner comprising: a light-beam emitter for emitting a light beam; alight-beam deflector for deflecting said light beam to scan a scanningsurface; a photo-detector provided at a position outside animage-forming scanning range of said scanning surface to detect ascanning light beam before said scanning light beam starts generating ascanning line, said photo-detector generating an output signal upondetecting said scanning light beam to determine a timing of commencementof writing said scanning line with respect to said scanning surface; andan optical member for deflecting said scanning light beam to be incidentupon said photo-detector in a direction to vary the timing of thescanning light beam incident upon said photo-detector.